| Summary of Background Data: Decompression and reconstruction of the cervical stability are the key points in the treatment of cervical diseases or injuries. It means that the surgeons need to remove all the compressive matters at different levels according to the different condition of different patients, and also have to choose suitable techniques of bone graft and fusion to maintain the stability of the cervical spine. The first one is responsible for the immediate clinical results and the second one will promise the better long-term outcome. Recently, the operation called"anterior cervical corpectomy and fusion (ACCF)"has been widely used in the treatment of cervical degenerative diseases, cervical injuries and cervical tumors in the clinical practice. After decompression, one kind method of autogenous local bone graft with titanium mesh cage (TMC) has been widely used, because it has the advantages of convenient employment, less related complications of harvesting bone block from the iliac crest and higher bone fusion rate. However, postoperative subsidence of TMC has been found in most patients with ACCF using TMC, which could lead to loss of cervical lordosis and intervertebral height, and even more subsidence-related complications, including neck pain, neurologic deterioration and instrument failure. The patients sometimes need revision surgery. At present, the design defects of the current TMC were widely considered as one of most important reason for the postoperative subsidence, which could be very difficult to be resolved by other salvage measurement. For this reason, a new type of full-contact TMC was designed to avoid subsidence and increase surgical results of ACCF.Objectives: To clarify the risk factors for the subsidence of the titanium mesh cage (TMC) after anterior cervical corpectomy and fusion, and to discuss their clinical correlation. On the basis of summary the defects of the current TMC and with the design of the modern bone grafting materials used in the cervical spine, to design and manufacture a new type of full-contact TMC, and make sure its safty and effect by a finite element study using computer simulation technique. The characteristics of stress distribution of new full-contact TMC were analyzed when compared with the current TMC.Methods: (1) A total of 120 patients with anterior cervical corpectomy and TMC fusion were included in the first part of this study. TMC subsidence, radiologic findings, and clinical results were evaluated in the 12-month follow-up period. Risk factors including age, sex, level of corpectomy, type of plate and using end caps were evluated, and also discuss the correlation of TMC subsidence with neck pain, neurologic deterioration and instrument failure. (2) The reasons for subsidence of TMC after ACCF were analyzed in the details in the second part of this study. On the basis of the study of defect of current TMC and reference to the anatomic data of normal Chinese patients such as the gradient of vertebral endplates in the cervical spine, a new type of full-contact TMC was designed and manufactured to avoid subsidence by enlarging the contact area of TMC and the vertebral endplates. (3) A finit element analysis was carried out to compare the biomechanical characteristics of two different kinds of TMC. The difference of stress distribution was recorded.Results: (1) After follow up, subsidence of TMC was found in 96 (79.7%) patients, including mild subsidence (1 to 3 mm) in 73 (60.7%) patients and severe subsidence ( > 3 mm) in 23 (19.0%) patients. Two-level corpectomy was more susceptible to severe subsidence when compared with 1-level corpectomy (p < 0.001). Japanese Orthopedic Association recovery rate for severe subsidence was significantly lower than that for no subsidence (p=0.010). Severe subsidence was correlated with subsidence-related complications, including neck pain, neurologic deterioration, and instrument failure. (2) The reasons for postoperative subsidence of TMC after ACCF could included osteoporosis, over remove of vertebral endplates, over distraction, no-match of TMC and vertebral endplate, small contact area and unsuitable clip of TMC. The first three reasons could be resolved by preoperative selection of patients and improve surgical technique during operation, but the inherent defects of the current TMC are difficult to be resolved. For this reason, the new type of full-contact TMC was designed with the design of the modern bone grafting materials used in the cervical spine. The new full-contact TMC used titanium allegation, which was structured by one main cylinder and upper and lower ending part. The main cylinder is similar with the current TMC and connected with the upper and lower ending part. The upper ending part is ring form and characterized by fornix formation in the sagittal plane. The lower ending part is also ring form and characterized by obliquity in the sagittal plane. Both the upper and lower ending part were thickened at the external ring to enlarge the contact area with vertebral endplates. With the consideration of different sizes of cervical vertebral body, the new TMC was designed with different sizes with the advantage of no more clipping before using it, which could be helpful to avoid subsidence of TMC. (3) Two finite-element models of C5 anterior cervical corpectomy and fusion with new and current TMC were reconstructed. Analytic results showed using new TMC could reduce the stress of TMC-endplate contact and anterior cervical plates, it also could reduce the relate displacement between C4 and C6 vertebrae.Conclusions: TMC subsidence was a common phenomenon after anterior cervical corpectomy and fusion with TMC. Severe subsidence might have led to bad clincial results and subsidence-related complications. The design defect of current TMC was one of the most important reasons for this problem and could not be resolved by other salvage measurement. The new full-contact TMC designed to enlarge the contact area between the TMC and vertebral endplates, which are useful in maintain of the cervical stability and avoidance of postoperative subsidence. |
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